Spending some time in OS X, one cat get quite used to that 3-finger-drag, which makes selecting and dragging anything soo much easier - just put three fingers on the touchpad and you're in the drag gesture already.
I have quite missed this on Linux, but with the mtrack touchpad driver, it is now possible to have. The original code for mtrack is on GitHub, but it has been recently forked by p2rkw and this fork comes with many new features added, one of them is 3-fingers-drag.
If you haven't heard of mtrack yet, it's an alternative to synaptics driver, originally with the goal to provide proper multitouch for MacBooks on Linux via the kernel multitouch protocol, since synaptics didn't have that yet at that time. Now it has grown into rather good synaptics alternative with many features for great multitouch experience (it has all gestures support right in the driver - pinch-to-zoom, finger-rotate, up to 5-fingers-swipe in all 4 directions etc plus palm/thumb detection and option to ignore those and/or disable the whole touchpad when palm/thumb is detected), but to have an actually good experience, some time spent on fine-tuning the config is still required. I'm still in the process of fine-tuning mine, but I'll post it once I'm really happy with it.
So if you're using mtrack, be sure to update to p2rkw's fork and to use 3-fingers-drag, add this to your touchpad config (xorg.conf or xorg.conf.d/):
Option "SwipeDistance" "1"
Option "SwipeLeftButton" "1"
Option "SwipeRightButton" "1"
Option "SwipeUpButton" "1"
Option "SwipeDownButton" "1"
Option "SwipeClickTime" "0"
Option "SwipeSensitivity" "1000"
It's also possible to have 4-fingers-drag, but that seems like a waste of fingers :)
Additionally mtrack works well with easystroke which is a gesture recognition for Linux, so one can set the various multitouch gestures to virutal buttons and then handle those buttons with easystroke. So in theory, if you want 3-fingers-drag only for window movement, it should be possible to map the 3-fingers-drag to alt+drag which would mean that putting 3 fingers down would allow to drag the window from anywhere, not just it's titlebar.
I've been using mtrack for about half a year on my Macbook Pro and it misses just two things to be absolutely perfect - that kinetic scrolling (swipe two fingers fast and it scrolls fast) and good cursor acceleration (slow finger movement moves the cursor slower and vice-versa), but I understand this is something to be set in X/XInput.
But overall, I'm quite happy with mtrack...only if it could have runtime config :)